Field
The invention relates to a medical device having a body which is tubular at least in some sections, can be transferred from a compressed state to an expanded state and has a circumferential wall with at least a first lattice structure and a second lattice structure. The invention further relates to a system having such a device.
Discussion of Related Art
DE 601 28 588 T2 discloses a stent whose tubular structure is formed by a plurality of layers. The individual layers each comprise a wire braid, the wire braids being interwoven. The wire braids of the individual layers are therefore in each case woven with the wire braid of an adjacent layer and thus form a connection between the layers that covers a large surface area. This results overall in a relatively complex braided structure of the wall of the stent.
The complex braided structure increases the fine mesh of the known stent, and this is intended to have advantages in the treatment of aneurysms. Specifically, the stent is used to impede the flow of blood into an aneurysm, by means of the stent being placed in a blood vessel in the area of an aneurysm. For this purpose, the stent is guided in a conventional manner known per se to the treatment site via a delivery system. The stent lies in a compressed state inside the delivery system. In other words, the stent has a minimal cross-sectional diameter in the delivery system. In the area of the treatment site, the stent is released from the delivery system. The stent is in particular expanded or widened at the treatment site, such that the stent bears on the vessel wall of the blood vessel. The expansion can take place automatically (self-expandable stents) or with the aid of a balloon of the delivery system (balloon-expandable stents).
The known stent has disadvantages. The complex braided structure, in which the individual wire elements are interwoven over a plurality of layers of the walls, means that, when the known stent is in the compressed state, the individual wires inside the delivery system are in an arrangement that requires a large amount of space. This arrangement is seen particularly in the cross section of the compressed known stent, which is shown by way of example in FIG. 6a. Here, the first wires 41 of a first braid layer have a larger cross-sectional diameter than the second wires 42 of a second braid layer. The first wires 41 of the first braid layer are interwoven with the second wires 42 of the second braid layer. In the compressed state, this results in the bulky arrangement as per FIG. 6a. Relatively large free spaces between the first and second wires 41, 42 remain unused, such that the known stent, in the compressed state, has a relatively large overall cross-sectional diameter. This also influences the minimum possible cross-sectional diameter for the delivery system. Delivery of the known stent into quite small vessels is thus made more difficult.
As a result of the interweaving of the individual layers, the flexibility of the known stent is also adversely affected. In particular, the interwoven wires become blocked on each other, such that the known stent has a comparatively high degree of stiffness or low flexibility.
In general, aneurysms in blood vessels are affected by various physical phenomena that can lead to an enlargement or even a rupture of the aneurysm. These physical phenomena, arising from the physiology of the cardiovascular system, comprise, on the one hand, the transfer of the blood pressure into the aneurysm and, on the other hand, shear stresses which are caused by a flow of blood inside the aneurysm, and also local loads which act on the aneurysm wall or aneurysm neck and are caused when individual areas of the aneurysm are attacked directly by the blood flow.
Aneurysms mostly form in arteries, i.e. blood vessels leading away from the heart. On account of the pulsating pump action of the heart, the blood flow in arteries is subject to intense fluctuations of pressure. The maximum pressure peaks in the arterial system occur in the ejection phase of the heart, the systole. A pressure minimum is reached in the diastole, the filling phase of the heart chambers. The level of the local pressure within defined sections of the vessels is determined by, among other things, the compliance, i.e. the elasticity, of the vessel wall. The pressure fluctuations in the vessel are transferred through the aneurysm neck into the aneurysm. If untreated, the pressure inside the blood vessel is transferred almost completely into the aneurysm, which leads to increased loading of the already weakened aneurysm wall. There is a danger of the aneurysm rupturing. The flow of blood from the blood vessel into the aneurysm is impeded by the use of known stents, for example the aforementioned stent according to DE 601 28 588 T2. A through-flow resistance is thus created which reduces the velocity of the flow of the blood into the aneurysm. Therefore, during the systole, the pressure inside the aneurysm rises more slowly and to a lesser degree than inside the blood vessel. In other words, the transfer of pressure from the blood vessel into the aneurysm through the meshes of the stent is delayed and incomplete. FIG. 1c shows an example of the pressure profile of the blood pressure in the blood vessel (solid line) and the pressure curve of the blood pressure inside the aneurysm (broken line).
It is known from practice that, some hours or days after an aneurysm has been treated with known stents that impede the transfer of pressure into the aneurysm, fissures can appear in the aneurysm wall and lead to bleeding. In the treatment of aneurysms with the known stents, there is therefore still the danger of the aneurysm rupturing.
It is assumed that, when the aneurysm is covered by known stents that influence the blood pressure in the aneurysm, the cells of the aneurysm wall, including muscle cells in the area of the muscle layer (tunica media) of the vessel wall, degenerate as a result of the diminishing load. In other words, the cells of the aneurysm wall are used to the high pressure load. When the high pressure load is lost, degenerative processes can set in, as a result of which the mechanical properties of the vessel wall may undergo negative changes. The danger of a rupture of the vessel wall in the aneurysm region thus increases.
The blood flow inside an aneurysm is subject to a further physical phenomenon. As the blood in the blood vessel flows past the aneurysm neck, shear forces act at the interface between the blood in the blood vessel and the blood inside the aneurysm. The resulting shear stresses cause eddying of the blood inside the aneurysm. A flow eddy thus forms in the aneurysm. The eddy formation in the aneurysm prevents blood clotting inside the aneurysm. In particular, the eddy formation prevents areas of stasis from developing, which are seen as a precondition for agglomeration in the form of so-called rouleaux formation. The expression rouleaux formation, or pseudoagglutination, designates the reversible formation of chain-like stacks of red blood cells. With regard to the aforementioned degeneration of cells of the aneurysm wall, the obstruction of a tangential blood flow, which on account of shear stresses leads to an eddying of the blood flow inside the aneurysm, is regarded as disadvantageous. Up to a certain point, however, reduction of the shear stress is necessary to ensure that the blood can clot. However, if the reduction is too great, thrombus development takes place too rapidly. The fresh clot developing as a result of the blood stasis rapidly increases in volume, which can lead to fissures in the aneurysm wall.
Aneurysms in curved blood vessel sections have a further peculiarity in terms of the way they are influenced by the blood flow in the blood vessel. The curved shape of the vessel causes the blood in the blood vessel to be deflected in a curved trajectory. When an aneurysm develops at the apex of the curve, a flow component of the blood flow arises which is oriented substantially directly into the aneurysm, in particular onto the aneurysm neck. The blood from the blood vessel thus flows directly into the aneurysm. As soon as the inflowing blood strikes the aneurysm wall, particularly in the aneurysm head, the blood flow is deflected, as a result of which the kinetic flow energy of the blood is converted into a local pressure that locally stresses the aneurysm wall. The local inflow, and the local pressure resulting from the latter, can, in conjunction with the physiological pressure wave triggered by the systole and the diastole, be the cause of the development of the aneurysm. A reduction of the pressure wave can be positive in order to prevent the aneurysm growing any further, or even in order to achieve shrinkage of the aneurysm. On the other hand, the reduction can have a disadvantageous effect on the degeneration of the cells of the aneurysm wall.
By means of known stents that cover the aneurysm neck, the local pressure caused by the direct inflow of blood into the aneurysm is reduced or avoided, since the blood flow through the stent placed in the vessel is deflected into the predetermined curved trajectory. The fraction of the flow component routed directly into the aneurysm is thus reduced. At the same time, the known stents avoid the transfer of a pressure wave into the aneurysm, as a result of which the degeneration of the cells of the aneurysm wall is promoted.
Another possible way of avoiding direct flow onto an aneurysm is to influence the vessel curvature. For example, the radius of curvature of the vessel in the area of the aneurysm can be reduced by a suitable stent. A precondition for this is a stent structure that has sufficient stiffness or radial strength to ensure that the stent structure forces the blood vessel into a more elongate and less curved shape.
In practice, the above-described medical requirements concerning the treatment of aneurysms are satisfied by a number of different technical approaches. On the one hand, it is assumed that a very fine mesh, i.e. the smallest possible mesh size, of an aneurysm stent permits efficient treatment. The very fine mesh is usually obtained using a large number of wires. In order to achieve suitable crimpability, such that the aneurysm stent can be inserted into small blood vessels, the individual wires have a comparatively small cross-sectional diameter. Therefore, stents of this kind develop a comparatively low radial force. This means that stents of this kind do not permit any influence of the curvature of a blood vessel. Moreover, stents with a low radial force have low stability, which results in the danger of the stent moving away from its original position inside the blood vessel on account of the blood flow or the pulsation. There is therefore the danger of dislocation of the stent. In particular, cases are known from practice in which the inserted stents have migrated out of the blood vessel into the aneurysm and have caused further damage there. On account of the comparatively low radial force, stents of this kind also have a relatively small restoring force. Frictional forces between the stent and the vessel wall can mean that it is not possible to ensure an adaptation of the cross-sectional diameter of the stent to the cross-sectional diameter of the blood vessel, particularly under the influence of the systole and diastole. With large braiding angles, the lattice structure can easily squash together. As a result, the cells become smaller and the lattice structure becomes tighter. The permeability decreases, and the through-flow resistance increases, which can impair the flow conditions and can lead to occlusion of side branches of the vessels.
In the known stents, the comparatively fine mesh is also achieved through a large braiding angle. A large braiding angle also increases the foreshortening. Foreshortening is understood as a phenomenon in which the lattice structure of the stent shortens in the axial direction during the expansion, i.e. during the transfer from the compressed state to the expanded state. A large braiding angle causes a quite considerable shortening of the stent during the expansion. The positioning of such stents is made more difficult. There is the danger of the stent being wrongly positioned. The effect of the foreshortening is also seen in connection with the change of cross section of the blood vessel during the systole and diastole. Even with comparatively small changes of diameter, the stent with a large braiding angle can experience considerable lengthening or shortening. This also causes a change in the cell configuration and in the mesh size of the stent. The reproducibility of the treatment is thus made more difficult. By means of a large braiding angle, a high degree of flexibility is made available in the known stent. However, with flexible stents of this kind, the elongation of a curved blood vessel in order to reduce the impulse on the aneurysm wall is not possible.
A further disadvantage of stents known from practice is that the stents narrow at least in some sections during elongation. Such an elongation of the stent in the axial direction can be caused by the sequence of systole and diastole. During the systole, the vessel diameter is widened depending on the vessel compliance. Moreover, an axial elongation of the blood vessel takes place at the same time. The axial ends of a stent which is positioned inside the blood vessel, and which bears on the vessel wall, move away from each other during the elongation of the vessel. According to the foreshortening effect, the elongation of the stent causes at least in some sections a reduction of the stent diameter. The stent structure can then lift away from the aneurysm or from the aneurysm neck, as a result of which the effect of influencing the flow is reduced. Moreover, a narrowing of the stent diameter, triggered by an elongation of the stent, can cause the contact between stent and vessel wall to be reduced, with the resulting danger of dislocation of the stent.
The object of the invention is to make available a medical device which permits efficient treatment of aneurysms and has improved crimpability. In particular, the device is intended to prevent a postoperative rupture of the aneurysm or a postoperative weakening of the aneurysm wall. It is also the object of the invention to make available a system having such a device.
According to the invention, a device and system are disclosed.
The invention is based on the concept of making available a medical device, comprising a body which is tubular at least in some sections, can be transferred from a compressed state to an expanded state and has a circumferential wall with at least a first lattice structure and a second lattice structure. The first lattice structure and the second lattice structure form separate layers of the circumferential wall. The separate layers of the circumferential wall are arranged coaxially one inside the other. Moreover, the separate layers of the circumferential wall are connected to each other at least at points, in such a way that the first lattice structure and the second lattice structure are movable relative to each other at least in some sections.
According to the invention, the first lattice structure and the second lattice structure form separate layers of the circumferential wall. Therefore, the lattice structures are not connected to each other over a large surface area, as they are in the prior art. Instead, the connection between the lattice structures is punctiform, such that a relative movement is permitted between the layers or lattice structures.
Punctiform connection means that the area of the two lattice structures where they are arranged loosely on each other is greater in terms of surface area than the at least one connection area or the punctiform connection areas between the two lattice structures, in such a way that a relative movement is possible between the two lattice structures. The at least one connection area or the punctiform connection areas do not form a continuous lattice structure. Instead, the connection area is locally limited. For example, the connection area can in each case comprise individual cells or meshes of the two lattice structures in the area of which the mechanical connection exists. The punctiform connection area can be limited to at most 4 cells or meshes of the first and/or second lattice structure, wherein either 4 or fewer cells of the first lattice structure are connected to any desired number of cells, in particular to more than 4 cells, of the second lattice structure. The same applies conversely for the second lattice structure. It is also possible that both lattice structures are connected to each other in the area of at most 4 cells. The connection with 3 or 2 cells is disclosed explicitly. The punctiform connection can also comprise, for example, the connection of individual lattice elements of the two lattice structures, in particular lattice filaments made of plastic or metal, for example lattice wires and/or strands composed of several filaments, or wires, which can be twisted together or parallel alongside each other, i.e. not twisted together.
A punctiform connection is therefore understood as a connection limited to a partial area or a partial surface of the lattice structure, wherein in particular the ratio between the surface area of the connected lattice structures and the surface area of the free lattice structures is such that the lattice structures can move relative to each other in the free area, in particular can move relative to each other unimpeded. The surface area of the connected lattice structures is smaller than the surface area of the free lattice structures. The at least one punctiform connection can be arranged within the lattice structure. The punctiform connection has an areal extent (one or more connection points) or a linear extent (one or more connection lines) and is surrounded on all sides, or at least on two sides, particularly in the linear extent, by lattice structures arranged loosely on each other. The punctiform connection can thus comprise at least one connection point, in particular several individual connection points each with an areal extent and/or at least one connection line, in particular several individual connection lines. A connection line can be formed from several individual connection points arranged in a row, in particular in the circumferential direction. The term connection point is not to be understood in the strict mathematical sense.
The punctiform connection can be arranged in the edge area, in particular at the edge of a lattice structure. The edge area as a whole can form the punctiform connection. The edge area forms an outer area which is arranged in the axial direction of the device and which is arranged at least outside the first intersection or the first cell segment of the lattice structure. The outer area can, for example, be the loop area of a braided stent. In a retractable braid with an obliquely tapering tip, as is described in DE 10 2009 056 450 or DE 10 2009 056 450, the content of each of which is fully incorporated by reference into this application, the area from the obliquely tapering tip to the in cross section cylindrically closed jacket area forms the edge area in which the lattice structures are connected. It is also possible to connect the lattice structures only at the oblique edge of the tip, for example by twisting the wires together.
If the punctiform connection is arranged at the edge of a lattice structure, the edge forms a limit of the connection. The other sides of the connection adjoin lattice structures arranged loosely on each other. Both lattice structures can each be connected at the edge, or one lattice structure at the edge and the other lattice structure away from the edge, for example in the middle area. This applies both to the first and also the second lattice structure.
It is also possible that the at least one punctiform connection is arranged outside the lattice structure, for example by connection strands or filaments or wires that extend over the lattice structures and are connected outside the lattice structures.
The punctiform connection can have different geometric shapes. For example, the shape of the connection can correspond to the shape of a cell or of several contiguous cells. Generally, the punctiform connection can be formed from individual subconnections, which for their part represent punctiform connections, for example in the form of individual wires or strands connected to each other at points. The higher-order punctiform connection is at least partially surrounded by lattice structures arranged loosely on each other, in such a way that, in the unconnected area of the lattice structures, a relative movement of the lattice structures is possible. This applies both to areal and also to linear punctiform connections.
The linear connection can extend in the circumferential direction and/or in the longitudinal direction and/or obliquely with respect to the longitudinal axis of the device. It preferably extends only in the circumferential direction or only in the longitudinal direction.
The length of the linear connection is at most 30%, in particular at most 25%, in particular at most 20%, in particular at most 15%, in particular at most 10%, in particular at most 5%, in particular at most 4%, in particular at most 3%, in particular at most 2%, in particular at most 1% of the total length of the device in the longitudinal direction or of the circumference of the device.
It is possible that the punctiform connection is arranged at the edge or even outside of the two lattice structures. For example, the two lattice structures can be connected by a common strand or guide wire by which the device can be actuated or can be moved in a delivery system. In this case, the two lattice structures are arranged loosely on each other across the entire surface area of the device and are fixed only at the axial end, where the two lattice structures are connected to the strand or to the guide wire.
The two layers or lattice structures are arranged coaxially one inside the other. This has the effect that the tubular body, in a compressed state, has a smaller cross-sectional diameter than in the prior art. Specifically, the invention provides for a regular arrangement of the individual wires or webs of the lattice structure, as a result of which the number of unused free spaces between the individual wires or webs is reduced. The crimpability or compressibility of the tubular body is thus increased.
By virtue of the double-walled structure, or the multi-layered design of the circumferential wall composed of mutually movable layers, it is possible to cover different application possibilities. Thus, in the device according to the invention, a division of functions can be provided in which one of the lattice structures has, for example, a carrying or supporting function, and the other or a further lattice structure has the function of influencing the flow in the area of an aneurysm.
The lattice structures or separate layers are connected to each other at points. The punctiform connection between the lattice structures ensures that the lattice structures substantially maintain their position relative to each other. In particular, the lattice structures maintain their relative position independently of a compressed or expanded state. Parts or sections of the lattice structures are able to move relative to each other. However, complete displacement of the two lattice structures relative to each other is prevented by the punctiform connection. In this way, the risk of dislocation of the medical device is minimized.
In a preferred embodiment of the medical device according to the invention, the first lattice structure and/or the second lattice structure is formed in each case from interwoven wires. Preferably, both lattice structures, or generally the lattice structures of the circumferential wall, each have a wire braid. The individual wire braids or lattice structures are therefore advantageously formed from several wires which extend in a spiral shape about a longitudinal axis of the tubular body. Wire spirals are provided that run in opposite directions and are interwoven. The individual layers of the circumferential wall are therefore formed by wire braids or interwoven wires or bands. However, the interweaving is present exclusively within an individual layer. The individual layers are interconnected at points, such that a relative movement between the layers is permitted.
It will be noted in this connection that the application does not only disclose and claim lattice structures that comprise a wire braid. Instead, the invention also includes lattice structures that are formed on the basis of lattice webs. Lattice structures of this kind can be produced, for example, by laser cutting or chemical vapor deposition.
In the context of the invention, provision is also made that each individual wire element of a lattice structure or of a layer comprises a single site at which the wire or the wires is or are connected to a wire or to wires of an adjacent layer. This has the effect that a punctiform connection exists between the layers.
The first lattice structure can have a proximal end, which is connected to a proximal end of the second lattice structure in such a way that distal ends of the first and second lattice structures arranged opposite the proximal ends are movable relative to each other. This embodiment goes back to the idea of interconnecting the lattice structures of the separate layers at in each case an axial end, in particular at the proximal ends. Thus, the entire lattice structure is movable between these. By contrast, the distal ends of the first and second lattice structures are arranged free, such that the distal ends of the lattice structure are movable relative to each other. The relative mobility of the lattice structures at least in some sections has the particular advantage of permitting a division of functions. In particular, the first and second lattice structures can have different geometries, such that different functions can be performed by the first and second lattice structures. The connection of the proximal ends of the lattice structures to each other is particularly advantageous, since the area where the lattice structures are movable relative to each other is quite large. In this way, different properties of the lattice structures can be combined across a relatively large area or the entire area of the tubular body. As an alternative to the connection of the proximal ends of the lattice structures, it is also possible that the distal ends of the first and second lattice structures are connected to each other. Moreover, the first and second lattice structures can be connected to each other at points in a middle area of the tubular body. The free ends of the lattice structures at the distal and/or proximal end of the device have the effect that the two lattice structures can shorten independently of each other during the expansion in the vessel (foreshortening), for example if the two lattice structures have different braiding angles.
It generally applies that a division of functions of the two structures is permitted by the only punctiform connection of the lattice structures.
According to another preferred embodiment, the first lattice structure and the second lattice structure, in a production state, have braiding angles that are the same at least in some sections or different from one another. Different braiding angles between the first lattice structure and the second lattice structure, or between the separate layers of the tubular body, have the effect that the lattice structures shorten to different extents during the expansion of the tubular body. Even in the event of a change of cross section of the hollow organ of the body in which the medical device is inserted, the lattice structures with different braiding angles behave differently. The different shortening of the lattice structures can be used advantageously for precise positioning of the medical device. For example, the second lattice structure can be designed in such a way that the effect of the foreshortening is reduced. The second lattice structure can therefore be positioned relatively exactly. Since the first lattice structure is connected to the second lattice structure at points, a precise positioning of the second lattice structure at the same time permits a relatively precise positioning of the first lattice structure or generally of the tubular body.
Preferably, the braiding angle of the first lattice structure and/or of the second lattice structure is at most 70°, in particular at most 65°, in particular at most 60°, in particular at most 59°, in particular at most 57°, in particular at most 55°, in particular at most 52°, in particular at most 50°. Such a braiding angle on the one hand ensures a sufficient flexibility of the lattice structures. On the other hand, such a braiding angle limits the foreshortening effect. Moreover, squashing together is reduced, such that the predetermined through-flow resistance is not impaired.
In a radially expanded state of the tubular body, a gap can be formed at least in some sections between the first lattice structure and the second lattice structure. Particularly in conjunction with different braiding angles for the first lattice structure and the second lattice structure, this ensures that, in the event of a change of the cross section or length of the hollow organ of the body in which the medical device is arranged, the two lattice structures lift away from each other. In this way, a gap is formed between the lattice structures, in particular an annular gap.
For example, the gap can be produced if the outer, second lattice structure or the outer net has, in the longitudinal direction, two spaced-apart, punctiform connections to the inner lattice structure, for example two connection lines extending in the circumferential direction, or individual connection points along two lines extending in the circumferential direction. The connection lines can be arranged at the axial ends of the lattice structure or can be offset axially inward from one or both ends. The two lattice structures have different braiding angles. The outer, second lattice structure has a smaller braiding angle and, therefore, a smaller foreshortening than the inner, first lattice structure. In the expanded state, the inner lattice structure is shortened to a greater extent than the outer lattice structure. This leads to an outward bulging of the second lattice structure and, therefore, to a gap between the two lattice structures. The difference in braiding angle can be at least 1°, in particular at least 2°, at least 3°, at least 4°, at least 5°, at least 10°, at least 15°, at least 20°, at least 25°, at least 30°. The upper limit for the range of the difference in braiding angle is at most 30°, in particular at most 25°, at most 20°, at most 15°, at most 10°, at most 5°, at most 4°, at most 3°, at most 2°, at most 1°. The aforementioned upper and lower limits can be combined with one another.
Generally, the bulge can occur between individual, axially spaced apart connection points, in particular between pairs of axially spaced apart connection points. It is possible to provide two longitudinally spaced apart connection lines composed of several connection points arranged in series in the circumferential direction. It is also possible to provide more than two such connection lines, between each of which a bulge is formed, such that several bulges are arranged in succession.
Flow eddies, which form a kind of cushion, develop in the gap between the lattice structures. The cushion leads to a desired loss of energy, such that the flow velocity is slowed down. The shear stresses in the main vessel thus act initially in the gap and generate the eddy there. The shear stresses transferred from the gap into the aneurysm via the wall of the net, or of the outer lattice structure, are thereby reduced. Clotting is promoted in the aneurysm. Moreover, the local pressure loads acting on the aneurysm wall and caused by the inflow of blood into the aneurysm are reduced.
Preferably, the first lattice structure and the second lattice structure each have closed meshes. The size of the meshes of the first lattice structure is advantageously different than the size of the meshes of the second lattice structure. In particular, the first lattice structure can have a smaller mesh size than the second lattice structure. In other words, the first lattice structure preferably has a finer mesh than the second lattice structure. The second lattice structure can, for example, form a carrier structure for the net-like structure of the first lattice structure. In this way, the division of functions between the two lattice structures or layers of the circumferential wall is ensured. The second lattice structure supports or fixes the first lattice structure in the blood vessel. By contrast, the first lattice structure can have such a fine mesh as to efficiently influence the flow of the blood into the aneurysm. Moreover, the first lattice structure can be flexible in such a way that the first lattice structure is easily able to follow a change of cross section of the blood vessel.
The wires of the first lattice structure preferably have a smaller cross-sectional diameter than the wires of the second lattice structure. The expansibility of the first lattice structure compared to the second lattice structure is thereby increased. Moreover, the first lattice structure can have a greater number of wires than the second lattice structure. This ensures that the first lattice structure has a finer mesh than the second lattice structure. In connection with a smaller cross-sectional diameter of the wires of the first lattice structure, the expansibility of the first lattice structure is further increased by comparison with the second lattice structure. The function of influencing the flow of blood into the aneurysm is improved.
Preferably, the first lattice structure forms an outer layer and the second lattice structure forms an inner layer of the tubular body. The second lattice structure can form a carrier structure, and the first lattice structure can form a net-like covering structure. The carrier structure supports the covering structure from the inside. This avoids a situation where the first lattice structure or the covering structure does not completely deploy upon expansion. The inner carrier structure, or the second lattice structure forming the inner layer, supports the first lattice structure across the entire length thereof.
In another preferred embodiment of the medical device, the first lattice structure has an axial lengthwise extent that is smaller than an axial lengthwise extent of the second lattice structure, in such a way that the first lattice structure covers the second lattice structure in some sections, in particular by at most 98%, at most 97%, at most 96%, at most 95%, at most 94%, at most 93%, at most 92%, at most 91%, at most 90%, at most 85%, at most 80%, at most 75%, at most 70%, at most 65%, at most 60%, at most 55%, at most 50%, at most 45%, at most 40%, at most 35%, at most 30%, at most 25%, at most 20%, at most 15%, at most 10%, at most 5%, relative to the longer lattice structure. The aforementioned geometric ratios relate to the production state of the medical device. The production state corresponds substantially to an unloaded state. This means that the medical device is not exposed to an external force causing a compression of the tubular body. In other words, the tubular body is fully expanded in the production state.
It is also possible to adapt the device such that the aforementioned geometric ratios are present in the compressed state, wherein the first lattice structure is shorter than the second lattice structure. The aforementioned values are also disclosed in connection with the compressed state.
The difference in length between the two lattice structures can be increased, decreased or maintained constant upon expansion through adaptation of the foreshortening by means of a suitable choice of the braiding angles. For example, the difference in length can be shortened by at least 10%, in particular at least 20%, in particular at least 30%, in particular at least 40%, in particular at least 50%, in particular at least 60%, in particular at least 70%, in particular at least 80%, in particular at least 90% or by 100% length equalization). On the other hand, the difference in length can be increased by at least 2%, in particular at least 5%, in particular at least 10%, in particular at least 20%, in particular at least 30%, in particular at least 40%, in particular at least 50%, in particular at least 60%. At length equality, i.e. when the starting difference is 0 mm, the aforementioned values relate to the total length of one of the two lattice structures.
In absolute values, the difference in length can be changed (decreased or increased) as follows: 1 mm, 5 mm, 10 mm, 15 mm, and 20 mm. In the case of the decrease of the difference in length, these values are lower limits (at least) and in the case of the increase they are upper limits (at most).
Preferably, the second lattice structure is covered at least in some sections by the first lattice structure. The tubular body therefore has at least one section that has a multi-layer design.
The tubular body can have at least a third lattice structure. The third lattice structure preferably forms, together with the first lattice structure, the outer layer of the tubular body or of the circumferential wall of the tubular body. Generally, the individual separate layers of the circumferential wall can have several lattice structures. The lattice structures of individual layers can be movable relative to each other. It is important that independent layers each comprise at least one lattice structure that is movable in some sections relative to a lattice structure of an adjacent layer. It is preferable if the outer layer has several lattice structures. In the compressed and/or expanded state of the tubular body, the lattice structures of the outer layer, i.e. the first and third lattice structures, can be arranged flush with each other. The cross-sectional diameter of the tubular body in the compressed state is thus reduced. Alternatively, the lattice structures of the outer layer, i.e. the first and third lattice structures, can be arranged overlapping in the compressed and/or expanded state of the tubular body. This allows the second lattice structure to be covered over a relatively large surface area in an expanded state of the tubular body.
Preferably, the first lattice structure is connected at a proximal end, and the third lattice structure at a distal end, to the second lattice structure which forms the inner layer of the tubular body. In other words, the first and third lattice structures each have an end fixed to the second lattice structure and also a free end, wherein the free ends of the first and third lattice structures are arranged facing each other or adjacent to each other. In the compressed state of the tubular body, the free ends of the first and third lattice structures can be arranged flush with each other or in alignment. The free ends of the first and third lattice structures can also overlap each other in the compressed state of the tubular body.
Provision is preferably made that the first lattice structure and the third lattice structure overlap at least in some sections in a radially compressed state or a radially expanded state. On account of the foreshortening effect, which acts not only on the first and third lattice structures, but in particular on the second lattice structure that forms the inner layer of the tubular body, a shortening of the inner layer or second lattice structure takes place during the expansion of the tubular body. The two lattice structures that form the outer layer, i.e. the first and third lattice structures, moves closer to each other during the expansion of the tubular body. By suitable design of the individual lattice structures, it is possible to ensure that the first and third lattice structures overlap in some sections in the expanded state of the tubular body. During the expansion, the free ends of the first and second lattice structures thus move closer to each other and push over each other. This is the case when the effect of the foreshortening of the outer lattice structure is less than the effect of the foreshortening of the inner lattice structure. Preferably, the overlapping area of the first and third lattice structures is arranged at the treatment site in the area of the aneurysm. This has the effect that the outer layer of the tubular body has an increased expansibility in the area of the aneurysm, since the free ends of the first and third lattice structures are movable relative to each other. Under the influence of the blood flow, the free ends of the first and third lattice structures or of the overlap areas are therefore able to bulge into the aneurysm, such that a flow cushion is formed between the outer layer and the inner layer or the second lattice structure in the area of the aneurysm, in which cushion the flow energy of the blood flowing into the aneurysm is reduced and, consequently, the load applied to the aneurysm wall is minimized. It is also possible that the first and third lattice structures overlap each other in some sections both in the radially compressed state and also in the radially expanded state. The lattice structures, or the inner layer and the outer layer, can be designed in such a way that the first and third lattice structures do not overlap in the radially expanded state of the tubular body. In other words, the free ends of the first and third lattice structures in the radially expanded state can be arranged flush on each other or spaced apart from each other. The first and third lattice structures can thus be arranged in alignment with each other in the radially expanded state of the tubular body.
In another preferred embodiment, provision is made that the first lattice structure and the third lattice structure each comprise a proximal end, which is connected to the second lattice structure. In this case, the proximal end of the first lattice structure can be arranged at a distance from the proximal end of the second lattice structure. The outer layer can generally comprise several lattice structures which each form an axial section of the outer layer. The lattice structures, in particular the first and third lattice structures, each have a proximal end which is connected at points to the second lattice structure, i.e. the inner layer. The distal end of the first and third lattice structures is arranged free. The first and third lattice structures can overlap each other. In this way, the first and third lattice structures can form a scale-like outer layer. In particular, the first and third lattice structures can have a valve function, wherein the first and third lattice structures are advantageously positioned in the area of an aneurysm. The free ends of the first and/or third lattice structures can be deflected radially outward with respect to the inner layer of the tubular body, such that a catheter, for example a catheter for the positioning of coils, can be inserted into the aneurysm, wherein the catheter is guided through the meshes of the second lattice structure and deflects at least one free end of the first or third lattice structure radially outward, in order to gain access to the aneurysm.
In another preferred embodiment of the medical device, provision is made that the first lattice structure comprises a middle section and two edge sections delimiting the middle section. In the middle section, the first lattice structure has a smaller braiding angle than in the edge sections. Generally, provision can be made that the braiding angle of the respective lattice structure is variable. In other words, the braiding angle can change along the lattice structure, particularly in the longitudinal direction of the lattice structure. Preferably, the braiding angle changes along the first lattice structure in such a way that a smaller braiding angle is present in the middle section than in the edge sections. This ensures that the first lattice structure in the middle section has a greater radial expansibility compared to the edge sections. The middle section of the first lattice structure can therefore be expanded in the radial direction further than the edge sections. The expansibility is a result of the local flexibility in the middle section. However, the term flexibility is used primarily for the bending behavior of the whole device or of the whole stent.
An elongation of the vessel section in which the medical device is inserted is compensated by the edge sections during the systole. It is thus ensured that the axial ends of the first lattice structure, in particular a free end of the first lattice structure, do not significantly change their position. The positioning of the first lattice structure is instead maintained. By contrast, the middle section with the smaller braiding angle can utilize the smaller foreshortening effect during the systole. Specifically, the middle section of the first lattice structure can shorten during an elongation and simultaneous widening of the vessel section. Preferably, the middle section is positioned at the level of the aneurysm or of the aneurysm neck. This ensures that the middle section of the first lattice structure can bulge into the aneurysm or into the area of the aneurysm neck during the systole. As a result of the small braiding angle, the change in length is not significant. Thus, the middle section of the first lattice structure contributes to transferring the systolic pressure from the blood vessel into the aneurysm at least to a certain degree, such that the cells of the aneurysm wall are still under a mechanical load. Degeneration of the cells in the aneurysm wall is thus avoided.
In a preferred embodiment, the distance between the outer layer and the inner layer varies in the expanded state of the body, wherein the distance alternately decreases and increases at least in some sections. Specifically, the outer layer, in the expanded state of the body, has an undulating contour at least in some sections. The undulating contour is particularly effective in slowing down the flow.
The outer layer can have alternately disposed peaks and valleys, wherein at least some, in particular all, of the valleys are connected to the inner layer and/or are preshaped, in particular preshaped by heat treatment, and/or have another braiding angle than the peaks. In the connection, particularly the mechanical connection, of the valleys to the inner layer, it can be advantageous to connect a single valley or more than 1 valley, in particular more than 2 valleys, more than 3 valleys, more than 4 valleys, in particular all the valleys, to the inner layer and fix them. The fixed valleys are arranged proximally, i.e. on the same side as the proximal end of the outer layer. The distal end of the outer layer, and any unfixed valleys on the distal side, are movable in the axial direction. In a particularly preferred embodiment, only the proximal end is fixed which can be seen as a half valley proximally from the first peak. All complete valleys including the distal end are free and movable.
The undulating shape can be preshaped by mechanical forming or can be embossed and forms the rest state. In the catheter line, the undulating shape is stretched out and, upon release, it returns to the undulating rest state or starting state. When using a shape-memory material, the undulating shape can be embossed by a suitable heat treatment, utilizing the shape-memory effect. By means of different braiding angles, the radial stability can be locally influenced, such that some areas widen easily (peaks) and some areas widen less easily (valleys). The aforementioned options for utilizing the undulating contour can be used singly or in combination.
According to a subsidiary aspect, the invention is based on the concept of making available a system for medical uses and with a delivery system which comprises a flexible delivery element, in particular a guide wire. The delivery element is connected or connectable to the device. The system is preferably adapted in such a way that the device can be drawn back into the delivery system.
The illustrative embodiments and advantages that have been described in connection with the medical device apply equally to the system having such a device.